The endplate is a circumscribed differentiated region of the sarcolemma whose limits in area is determined by the nerve supply. The research program proposes to study systematically protein synthesizing activity associated with three discrete regions of th sarcolemma, viz., endplate, intermediate region and the musculo-tendonous region from (a) innervated, (b) denervated and (c) reinnervated fast muscle. In addition, it is proposed to ascertain whether RNA is associated with the sarcolemma, and, if so, to characterize the membrane RNA by microgelfractionation and to ascertain what classes are turned over in normal and denervated muscles. Finally, RNA classes synthesized in vitro of whole denervated and innervated muscles will be characterized by macrogelfractionation.